Really? Where was the Vesta (Aventine) seen? Ive read the Destiny series but have never seen it on screen.

The canon restriction is gone the day the Vesta went on sale

It actually already went out of the window with the Luna.
However with those two ships the situation is a bit different because they're not from another game company (=potential competitor) or someone who does not really exist any more (like Microprose) and it's also in some ways a method for Pocket Books to promote the ships that are featured in their books.
But despite this, it still took Cryptic god knows how long to get the Vesta ingame.

So while stuff from Pocket Books is at least possible, stuff from everyone else seems to be beyond Cryptic's reach.

I also fear the response to stuff like the Qang class (with soft-canon conditions similar to those of the Luna) will probably be "not worth the effort".

I don't want T6 ships. I don't want to scrap ships I paid for. I would rather see more t5/ t5.5 ships. Gorn cruisers/escorts. Nausicaan fligth deck cruisers. Orion escorts and cruisers.
SOMETHING for Letheans/silly cat race.
And the K'Vort, a full blown escort with boff layout of mirror Qin, 5 tac consoles and 15?/s turnrate.

I don't want T6 ships. I don't want to scrap ships I paid for. I would rather see more t5/ t5.5 ships. Gorn cruisers/escorts. Nausicaan fligth deck cruisers. Orion escorts and cruisers.
SOMETHING for Letheans/silly cat race.
And the K'Vort, a full blown escort with boff layout of mirror Qin, 5 tac consoles and 15?/s turnrate.

I could possibly back this IF it had the same paper-thin shield multiplier of all other BoP's. Otherwise leave this accident of poor special effects direction in CBS's archives.

Is only an excuse and does not explain why the Devs can create non-cannon favorite vessels for the feds and not for the KDF.

I can't spend any money in STO if they do not create merchandize to be consumed.
Supply and demand can't get any more simple.

I agree, with that excuse, any new KDF ship will not be worth the effort. Ships like the Qang can be anything that the Devs chose it to be. The Vesta and the Luna were not science-specific ships. I would at least like to see a +1 Tac ship. and the closest one does even comes close to the Fed one(s).

Well, we know that the devs are working towards a Tier 6 project, likely a command and control ship which would allow you to use your other ships by promoting officers. So in a sense you get the best of both worlds - a fleet admiral commanding his own small task force based on ships in his collection.

And if non-cannon sources are allowable by CBS, then why not look at the ships from Federation & Empire?

The Klingon B2 Dreadnaught. Largest built by the empire - so large in fact only 2 were completed, and the third was used only half built. Essentially it was a battleship who's forward command area could separate and operate as a battlecuiser. It looked like the old D7, but was 8-10 times larger. If memory serves, it was designed to take on starbases and win.